This application relates generally to testing systems for magnetic media storage devices and more particularly to testing read/write head elements prior to final assembly of the storage device.
The need for more efficient data storage devices has become critical with the staggering pace of advances in computer technology. The most common data storage device used today is the disc drive. Most disc drives are composed of one or more magnetic media discs attached to a spindle. A spindle motor rotates the spindle and discs at a constant high speed. An actuator assembly adjacent to the disc(s) has actuator arms extending over the discs, each with one or more flexures extending from each actuator arm. A read/write head is mounted at the distal end of each of the flexures. The read/write head includes an air bearing slider enabling the head to fly in close proximity above the corresponding surface of the associated disc. Information is stored on and retrieved from the magnetic media discs via the read/write head.
A flex assembly provides the requisite electrical connection paths for the actuator assembly while allowing pivotal movement of the actuator assembly during operation. The flex assembly includes circuitry to which head wires are connected; the head wires being routed along the actuator arms and the flexures to the heads. The flex assembly typically includes circuitry for controlling the write currents applied to the heads during a write operation and a preamplifier for amplifying read signals generated by the heads during a read operation. The flex assembly terminates at a flex bracket for communication through the base deck to a disc drive printed circuit board mounted to the bottom side of the disc drive. The actuator assembly and the flex assembly are usually combined before the disc drive is assembled. The product of this combination is called the head stack assembly (xe2x80x9cHSAxe2x80x9d).
Disc drive manufacturers are attempting to increase the amount of information stored on existing disc drives to meet the increased demand for information storage. Manufacturers have, for example, increased the areal density of their disc drives to fit more information on a constant sized disc. Areal density is a measurement of the number of bits of information that can be stored on one square inch of disc space. Increased areal density, however, requires a sophisticated read/write head to access information stored on the disc media. Some current disc drives use a dual element transducer head to overcome some of the problems encountered with increased areal density. One element is used to read data and a second element is used to write data in a dual element transducer head. Some disc drives utilize a xe2x80x9cmixedxe2x80x9d technology head design. In a mixed technology head, the read element transducer is of the magnetoresistive (MR) type, whereas the write element transducer is of the inductive type.
A HSA, as mentioned above, usually consists of heads, flexures, actuator arms, head wires, and a flex assembly with a preamplifier. Many processing steps are required to manufacture a HSA. The likelihood that the delicate read/write heads will be damaged increases as each processing step is completed. Electrostatic discharge or physical contact between the head and some other mechanical part, for example, may damage the sensitive read/write elements of the head. As a result of this damage risk, a manufacturer must verify that the read/write heads operate properly before placing the HSA into a disc drive. Current verification methods, however, are time consuming, expensive, and subject the heads to an additional risk of damage.
Dynamic electrical testing is the most common method of testing mixed technology heads. The HSA is placed in a dynamic electrical tester (xe2x80x9cDETxe2x80x9d). A DET simulates actual disc drive operation by placing the HSA within a magnetic media cylinder and then spinning the magnetic media cylinder at high speed. The magnetic media cylinder is basically a stack of one or more discs that imitates the disc, or discs, in a disc drive. A signal, sent by the DET through the HSA""s inductive write head element, is stored on the magnetic media cylinder. Next, the DET uses the HSA""s MR read head element to retrieve the data written by the inductive write element. A determination of whether the head elements are functioning properly can be made by comparing these two signals. Although very accurate, dynamic electrical testing is time consuming, expensive, and potentially destructive (the heads can be destroyed if they come in contact with the media being spun at high speeds).
Another method of testing a HSA is called static testing. In static testing, the HSA is placed within a changing magnetic field; the variation of the magnetic field induces small signals within the head elements. These signals are then sent through the preamplifier. A signal analyzer connected at the output of the preamplifier reads the signals. Static testing, although faster, cheaper, less complicated, and less destructive than dynamic testing, has its own inherent limitations.
Current static testing methods, for example, do not allow for amplitude or resistance testing of the write head. The only tests currently available for the write head during static testing are those provided by the preamplifier vendor, such as a write unsafe (xe2x80x9cWUSxe2x80x9d) or a fault (xe2x80x9cFLTxe2x80x9d) test among others. The outputs of the preamplifier are monitored when using current static testing methods. A logic high on the FLT pin, for example, may indicate that a low write data signal exists at the write head, the write head is shorted to ground, the write head was illegally selected, the write head is an open circuit, or low DC power is present at the preamplifier among others. Current static testing does not allow the write head amplitude signal to be analyzed, instead, dynamic testing must be used to analyze this signal.
The need to design a xe2x80x9creceiverxe2x80x9d for the write element is a second limitation of static testing. The write signal, using current static testing methods, must be xe2x80x9cwrittenxe2x80x9d to something in order to test the write head. The magnetic media cylinder is used in dynamic testing, however, such a magnetic media is not used in static testing. Instead, a receiver is used. The receiver is designed to mimic the characteristics of the magnetic media. The write signal is analyzed at the receiver to determine the characteristics of the write element. A large amount of money and time must be invested to design the receiver and its supporting circuitry for current static testing methods. It is in respect to these considerations and others that the present invention has been made.
In accordance with the present invention, the above and other problems are solved by a testing system that does not require dynamic testing and permits the use of a low frequency magnetic field to test the inductive write head elements. In a preferred embodiment of the present invention, the completed head stack assembly (xe2x80x9cHSAxe2x80x9d) is placed in the test apparatus. Test probes are aligned and placed in electrical contact with the electrical leads coming from each head element, between the head elements and the preamplifier. The HSA is then placed in a changing magnetic field. The changing magnetic field induces electrical signals within the inductive write head element. The condition and characteristics of the inductive write head element can be determined by analyzing the induced electrical signals.
In accordance with other aspects, the present invention relates to a method of testing an inductive write head element in an assembled HSA by placing test probes in electrical contact with the electrical connections of the inductive head element, between the inductive head element and the preamplifier, generating a changing magnetic field around a portion of the inductive write head element, inducing a test signal within the inductive write element, and analyzing the test signal induced in the inductive write element and determining whether the inductive write element is functioning properly.
Furthermore, the present invention eliminates the problems associated with static testing. Testing an inductive write head as a reader, for example, allows the same low frequency magnetic field that is generated to test the read head to be used for testing the inductive write head. The amplitude of the signal induced in the inductive write head and the resistance of the inductive write head can be measured directly, before the signals enter the preamplifier. The testing limitations imposed by the preamplifier vendors are therefore eliminated without resorting to dynamic testing.
Additionally, the present invention eliminates the need to design a receiver for testing the inductive write head. The same low frequency signal that is used to test the read element is used to test the inductive write element. The need to write a signal to the magnetic media, or to a receiver that mimics the magnetic media, is therefore eliminated. The large investment of money and time need to design the receiver and supporting circuitry is also eliminated.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.